1. Field of the Invention
This invention relates to a detachable fastening means for removably joining a first article to a second article and more specifically relates to a detachable fastener for joining impressions of a mouth formed of a lower mouth model and an upper mouth model onto a dental articulator. The detachable fastener is adapted to respond to a separating force to enable the mouth models to be removably separated from their adjacent support member forming a part of the dental articulator.
2. Description of the Prior Art
It is well known in the art to utilize apparatus for supporting impressions of mouths including teeth wherein the impressions comprise a lower mouth model and an upper mouth model. The mouth models are adapted to be positioned in a contiguous relationship upon each other to provide centric, lateral and protrusive movements relative to each other. Typically, the lower mouth model and upper mouth model are supported by a dental articulator horizontal base member and a horizontal top member, respectively.
Generally, impressions of a mouth can be categorized into three groups. The first group is where there is a complete absence of teeth which is referred to as either a toothless model or an edentulous model. The second group is where anchor teeth are missing requiring a removable partial denture and this is referred to as a partially edentulous model. The third group is where some teeth are missing but there are sufficient anchor teeth remaining for crowns and inlays and is referred to as a fixed bridge model.
The process of making an impression of a mouth and the fabrication of partial dentures, fixed bridges and crowns in a dental laboratory is a slow, multi-step process. Typically a dentist takes an impression of a patient's mouth and forms an original casting, which is normally fabricated in plaster of paris. The original casting is delicate and will not withstand the application of heat and absorbs a large quantity of moisture during fabrication of a more permanent type of impression. Accordingly, a wax model is made from the original casting and a refractory model is formed using an appropriate refractory material which is cast by a centrifuge technique. Thereafter, the cast refractory model is cured by placing the same in boiling water. The cast refractory model is then attached to a layer of binding material formed on the dental articulator by use of a material known as dry lute with sticky wax.
In order to register either the upper or lower mouth model to the articulator and to obtain the desired alignment or occlusion between the upper and lower mouth models, keying grooves are cut in each mouth model in the bottom surfaces, opposite the mouth impressions. The keying grooves are lubricated with a separating media, such as for example soap, and placed onto a curable binding material, such as for example, soft plaster of paris.
As the curable binding material is cured and the mouth models dry, shrinkage occurs therebetween which results in slight errors being introduced into the occlusion between the upper and lower mouth models.
After the curable binding material is cured and is hard, the mouth models are removable from the binding material because of the presence of the separation media. In the fabrication of partial dentures, bridges and crowns, the mouth models must be removed from the dental articulator many times. A "sticky wax", formed of rosin, bees wax and other waxes, may be applied to the keyed grooves to act as an adhesive or intermediate binding material to hold the mouth models in place on the dental articulator.
Accordingly, many devices have been developed to permit removable attachment of the mouth model to a dental articulator.
One known technique is to attach a metal plate to the mouth model and use a removable pin which passes through a hole in the plate and the dental articulator to attach the mouth model to the dental articulator. Magnetic fastening devices are known wherein a magnetic field is utilized to clamp the mouth model to a dental articulator. Other known means for attachably supporting dental models to a dental articulator are disclosed in U.S. Pat. Nos. 2,765,533; 2,608,762; and 2,571,280.
In the fastening means adapted for use with a dental articulator disclosed in the above referenced Patents, a single ball and joint arrangement is utilized wherein a clamping plate or the like is joined to a surface of an upper mouth model or lower mouth model. The clamping plate includes means for forming one part of the ball and socket joint. A support arm, which forms the dental articulator, includes the other part of the ball and socket joint.
In each of the means for attaching the mouth models to the dental articulator disclosed in the above referenced U.S. Patents, the articulators are constructed to have a single ball and socket joint as a supporting means for the entire dental model and plaster base to be supported thereby. The size of the ball and socket joint is relatively large in order to support the entire weight of the mouth models and to align the mouth models relative to each other on the dental articulator itself.
In the dental articulators of U.S. Pat. Nos. 2,765,533 and 2,608,762, the support plates are affixed or attached to the mouth models by means of fasteners or adhesive. The dental articulator disclosed in U.S. Pat. No. 2,571,280 is attached to the dental articulator base through a binding layer of plaster of paris.
U.S. Pat. No. 3,694,919 discloses another form of a dental articulator which utilizes a pair of spherical styluses supported above lateral truss portions and above a vertically extending shank extending from the base of the articluator. The spherical styluses and truss portions form a pivotable support point between an upper member of the dental articulator which supports an upper mouth model and a vertically extended support which extends from the horizontal base member which is adapted to support the lower mouth model. In essence, the spherical styluses cooperate with a spherical stylus receiving socket within the lateral truss portion to permit relative movement of the horizontal top member of the dental articulator relative to the horizontal bottom member of the the dental articulator. Mouth models are affixed to the dental articulator by means of a screw which extends from the horizontal base member of the dental articulator into an aligned threaded aperture formed into the lower adjacent surface of the dental model. The mouth model is removably attached to the lower or base member of the dental articulator through the threaded connection.
The use of ball and socket joints as a fastening means for various other applications is well known in the art. Typical of such other applications are those disclosed in U.S. Pat. Nos. 4,044,725; 2,791,454 and 2,717,792, all of which disclose various embodiments of a spherical member and a cooperating socket member to form various types of ball and socket joints.